The present invention relates to a semiconductor device and a manufacturing method thereof, particularly to a technique effective when applied to a semiconductor device having a semiconductor chip and a substrate connected via a stud bump.
In semiconductor devices, as miniaturization of semiconductor chips proceeds, the number of circuits to be mounted on one semiconductor chip is increasing. For such highly integrated circuits, semiconductor devices need a larger number of connecting terminals. For example, with advance in miniaturization, semiconductor memory devices have a higher capacity and has a bus width enlarged enough to process a large capacity of data at high speed, which require more connecting terminals.
To cope with such an increase in the number of connecting terminals, BGA (Ball Grid Array) type semiconductor devices adopt C4 connection (controlled Collapse Chip Connection) in which ball- or column-shaped bump electrodes using a solder and disposed horizontally on a surface on which a semiconductor device is to be mounted are connected simultaneously by vitrification of the bump electrodes 5 to a mounting substrate having connecting terminals formed thereover to correspond to the terminal disposal on the semiconductor device. The semiconductor device is connected to the mounting substrate by reflow soldering, that is, by heating the substrate by hot air blowing or infrared ray irradiation to melt the solder of the bump electrode and connect the bump electrode of the semiconductor device to the terminal of the mounting substrate, and then solidifying the solder by lowering the temperature.
Moreover, to meet a tendency to size and thickness reduction of an electronic device to be mounted, semiconductor devices are requested to have a smaller and thinner product size. Various types of semiconductor devices are considered as a CSP (Chip Size Package) semiconductor device in which the outside dimension of the product is made substantially equal to that of a semiconductor chip to be mounted.
A semiconductor device using a tape substrate is one of CSP. In this semiconductor device, a semiconductor chip is mounted on one side of a tape substrate having interconnects made of a metal film such as copper formed over a base made of an insulating resin such as polyimide; a bump electrode which will serve as an external terminal of the semiconductor device and is used for the connection with a mounting substrate is formed on the other side; and the semiconductor chip is connected with one end of the interconnect formed over the tape substrate and the bump electrode is connected to the other end.
Such a connection between the semiconductor chip and interconnect by using the bump electrode enables a reduction in inductance and in turn, speedup of signal processing, compared with the conventionally and popularly used connection by wire bonding. This also actualizes size and thickness reduction of the semiconductor device as a product.
Formation of bump electrodes using a solder is accompanied by an increase in the number of steps and a cost rise, because a solder paste is printed and adhered to a pad 12 through a mask, the solder thus adhered is melted by reflow and then, the residue such as flux is removed by washing. In addition, when a semiconductor chip and a substrate are connected via a solder, the melting point of the solder used for connecting the semiconductor chip with the substrate is set higher than that of another solder used for connecting a tape substrate and a mounting substrate, which inevitably limits materials used for these solders.
To overcome the above-described problem, a stud bump is considered as a measure for facilitating the formation of bump electrodes by making use of a wire bonding technique. In the formation of a stud bump, a gold wire having a diameter as fine as from about 20 μm to 30 μm and exposed from a wire bonder capillary is melted by using a discharge torch or the like. The molten gold becomes a sphere having a diameter of about 50 μm to 80 μm by surface tension. While the resulting gold ball is bonded onto the pad 12 of the semiconductor chip 4, the capillary is detached without reeling out a wire. The gold ball portion is separated from the capillary and a protruding electrode is formed on the pad 12.
In this stud bump, the spherical portion fixed onto the pad 12 has a diameter of from about 60 μm to 90 μm and a height of about 70 μm. Since the gold wire is drawn and the diameter of the wire decreased gradually upon separation, a conical protrusion is formed on the sphere.
In the connection between this stud bump and the tape substrate, the semiconductor chip is fixed by adhesion to the substrate with an adhesive layer such as NCF (Non Conductive Film) which is a film adhesive while pressing the semiconductor chip towards the substrate. The contact conduction is thereafter maintained between the stud bump and the connection terminal on the substrate.